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Study Shows Why the Heart's Not in Shift Work

People who work a rotating shift schedule that includes staying up all night may be causing harm to their heart, Italian researchers report.

It appears the heart would rather be taking a rest at night, which may explain why shift workers are at greater risk of heart disease and other problems.

"Shift work is associated with an increased rate of heart disease and accidents," said lead author of the study Dr. Raffello Furlan of the University of Milan in Italy.

In their study, the researchers monitored the hearts of 22 healthy male shift workers.

These men worked a 5-day rotating shift schedule of three different shifts: 6 a.m. to 2 p.m.; 2 p.m. to 10 p.m.; and 10 p.m. to 6 a.m.

Under normal conditions, when people sleep at night and work during the day, the body''s nervous system peaks in the morning and stays high throughout the day.

During this time, chemicals in the body are released that help drive the digestive system, breathing and other functions, according to the American Heart Association (AHA).

At night, the nervous system goes into a decreased activity mode, which allows for sleep.

According to the study findings published in the Oct. 17 issue of Circulation: Journal of the American Heart Association, shift work had only a minor impact on the body''s built-in clock that controls the nervous system.

The investigators found that the normal morning increase of nervous system activity was present regardless of work schedule.

"This resistance of the body''s internal clock to change with varied work schedules indicates that people don''t adapt as easily as we think to shift work, and could explain why shift workers are at higher risk" of heart disease, Furlan explained in a statement from the AHA.

The authors suggest that the conflicting messages that the heart is receiving -- the person''s desire to be up and doing physical work despite the body''s built-in clock, which causes it to rest -- may "play a role in the excessive rate of cardiovascular diseases in shift workers."